B. aplustre. The streamer-like Bulla. Pl. [17], fig. 7.
Species completely involute; the spire very distinct, visible, but not projecting, with a kind of thickening at the anterior part of the columellar edge.
B. lignaria. The woodlike Bulla.
Species sub-involute, no visible spire either within or without, but narrowed towards the top when it is slightly umbilicated; yellowish brown colour, with transverse pale striæ.
B. hydatis. The watery Bulla.
Species more solid, thicker, almost entirely involute; whorls of the spire slightly visible in an umbilicus projecting interiorly from the summit.
B. naucum. The sea-nut Bulla.
Species thin; the whorls of the spire visible externally, but without projection, and with a suture as if caniculated without thickening at the anterior part of the columellar edge.
B. fragilis. The fragile Bulla.
Species very thin, rather involute; the whorls of the spire distinct within as without; the suture deep, angular, and cleft in a greater or less part of its length.